Skin is the primary barrier that withstands environmental impact on a person's body. The environmental impact results from elements such as sun, cold, wind, humidity and other conditions. The environmental factors along with aging cause the skin to lose its youthful look and develop wrinkles. This phenomenon is known as skin ageing.
FIG. 1 is a schematic illustration of a side sectional view of a piece of human skin 100 and its underlying layers. Human skin 100 is made up from the epidermis 20, which is about 100 μm thick including its outermost layer the stratum corneum 10. The epidermis is followed by the dermis 30, which may extend up to about 4 mm from the surface. Subcutaneous layer 40 is located under dermis 30. These three layers control the overall external appearance of the skin (e.g. youthful or aged). The dermis 30 is made up of elastin, collagen 70, glycosoaminoglycans, and proteoglycans. The subcutaneous layer 40 includes fatty areas with fibrous vertical bands that course through it and form a link between dermal collagen 70 and subcutaneous layer 40. Collagen 70 provides the resilience and elasticity to skin. Age and sun exposure, reduce fibroplast metabolism and cause the collagen 70 to lose their elasticity and tensile strength, so that the skin loses its youthful, tight appearance.
Below subcutaneous layer 40 are located muscles 50 and muscle nerves that also contribute to the wrinkled appearance of the skin with age.
Numerous techniques have been described for skin rejuvenation by counteracting the above phenomenon, for example:
The most popular and widely used treatments for skin rejuvenation are dermabrasion peels, laser peels and chemical peels. These types of peels cause mild injury to the skin that is not too deep but yet deep enough to induce healing. The skin with its natural ability to repair itself initiates a process of rejuvenation thereby repairing the damage caused and improving the cosmetic appearance.
Dermabrasion is a method of removing skin by way of polishing or sanding. Once the old skin is abraded, a fresh layer of skin replaces the old one which has been removed.
In chemical peeling, a chemical solution is applied to the skin thus prompting the upper most layer of skin to peel off. Once the old layer of skin is removed a fresh layer of skin, which is better in color and blemish free, is formed replacing the peeled off layer. Different types of chemical peels enable achieving mild, moderate or deep peels suitable for different patients needs. A mild peel is a procedure that removes the superficial skin layer. This chemical peel involves a diluted acid solution, which normally stays on the skin for a few minutes. The Medium Peel procedure goes a little beyond the superficial layer of the skin. The chemical solution, as compared to mild peels, is kept on the skin for a longer time. Unlike the mild and medium-depth peel, a deep chemical peel penetrates deeper in the dermal layer to address more pronounced skin pigmentations and wrinkles.
One major disadvantage of these peeling methods is that after any peel and during the healing process, the treated area may become crusted resulting in skin pigmentation problems. Thus difficulties to control the depth of the peeling, possible pigment change, and risk of scarring are among the risks associated with chemical peeling.
The above mentioned methods suffer from being invasive and involving significant discomfort, pain, downtime and potential side effects. As these cosmetic procedures are all elective procedures, pain and the occasional side effects have been a significant deterrent to many potential customers, who would otherwise like to deal with skin problems.
To overcome some of the issues associated with the invasive procedures, laser and radio frequency energy based wrinkle reduction treatments have been proposed. For example, U.S. Pat. No. 6,387,089 describes a procedure referred to as photo rejuvenation, wherein pulsed light is used for heating and shrinking the collagen and thereby restoring the elasticity of the skin. Since collagen is located in the dermis, lasers that target collagen must penetrate through the epidermis and through the dermal epidermal junction. Due to Bier's Law of absorption, the laser beam is typically most intense at the surface of the skin. This results in unacceptable heating of the upper layers of the skin. Various approaches have been described to cool the upper layers of the skin while maintaining the layers underneath at the desired temperature. One approach is to spray cryogen on the surface so that the surface remains cool while the underlying layers (and hence collagen) are heated. Such an approach is described in U.S. Pat. No. 6,514,244. Another approach described in U.S. Pat. No. 6,387,089 is the use of a cooled transparent substance, such as ice, gel or a crystal that is in contact with the surface of the skin. The transparent nature of the coolant would allow the laser beam to penetrate the different skin layers while maintaining an acceptable temperature level on the surface of the skin.
Photo rejuvenation requires the use of intense pulses of filtered light. The light penetrates the outer skin layers, causing them minimal damage, and is absorbed by deeper tissues. Photo rejuvenation is useful only in treating fine to moderate wrinkles.
Photo rejuvenation risks include swelling, scarring, blistering, hyper/hypo pigmentation, sensitivity to sun exposure and sensitivity to make-up. Individuals with darker skin tones may suffer from hyper pigmentation for several months following treatment. During the recovery stage sun exposure must be avoided to minimize side effect such as hyper pigmentation.
Extensive sun exposure may lead to chronic UV irradiation. This appears to trigger dysfunctional wound repair pathways in the skin that involve gradual replacement of normal epidermal and dermal structures with characteristic atrophy and accumulation of elastotic dermal matrix components.
Currently, reversal of photo-aging is attempted by imparting cutaneous injury that induces new dermal collagen formation. Such cutaneous injury could be accomplished using mechanical (e.g., dermabrasion), chemical (e.g., retinoids and acid peels), or laser treatments. These cutaneous injuries are expected to intiate normal fibro-proliferative responses of the upper reticular and papillary dermal compartments, resulting in rejuvenated skin. U.S. Pat. No. 6,120,497 describes thermally injuring collagen in the targeted dermal region to activate fibroblasts. The fibroblasts in turn deposit increased amounts of extracellular matrix constituents. However, epidermal injury associated with a mechanical surface ablation process such as dermabration or peeling. Promotes the inflammatory phase, which inhibits the rejuvenative process. Hence, while the currently used methods, which are mentioned above, for intiating normal fibro-proliferative response of the dermal compartments can yield rejuvenated skin, due to the epidermal injury that occurs with these processes, the rejuvenative process is compromised.
An objective of nonablative photorejuvination is to induce a thermal wound repair response in the papillary and upper reticular dermal compartments (approximately 100-400 μm below the surface of the skin) while sparing the epidermal compartment. To spare the epidermis, one typically uses low fluences (laser energy densities). Unfortunately, such low levels are generally inadequate to promote the kinds of stimulation that are required to cause the desired dermal effect. Thus, prior art approaches result in low efficacy. In most cases, low dermal matrix remodeling and clinical responses (e.g., wrinkle reduction, retexturing, dyschromia reduction, and telangiectasia removal) are achieved by these procedures. Thus there is an unmet need for sparing the epidermal layer, but achieving enough stimulation of dermal matrix remodeling to be clinically effective.
To overcome some of the problems associated with the undesired heating of the upper layers of the skin (epidermal and dermal), U.S. Pat. No. 6,311,090 describes using RF energy and an arrangement comprising RF electrodes that rest on the surface of the skin. A reverse thermal gradient is created that apparently does not substantially affect melanocytes and other epithelial cells. However, even such non-invasive methods have the significant limitation that energy cannot be effectively focused in a specific region of interest, say, the dermis 30.
Electrosurgical resurfacing involves the use of a micro-electrical radio frequency that delivers energy to the skin. This treatment can be effective in eliminating or improving minor to moderate skin imperfections.
Other approaches have been described to heat the dermis without heating more superficial layers. These involve using electrically conductive needles that penetrate the surface of the skin into the tissue and provide heating. U.S. Pat. Nos. 6,277,116 and 6,920,883 describe such systems. Unfortunately, such an approach results in widespread heating of the subcutaneous layer and potentially melting the fat in the subcutaneous layer. This leads to undesired scarring of the tissue.
One approach that has been described to limit the general, uniform heating of the tissue is fractional treatment of the tissue, as described in U.S. Patent Application publication No. 2005/0049582. This application describes the use of laser energy to create treatment zones of desired shapes in the skin, where untreated, healthy tissue lies between the regions of treated tissue. This enables the untreated tissue to undergo a healing and recovery process.
As opposed to traditional laser resurfacing, which treats the whole surface of the target tissue, fractional laser skin resurfacing uses fractional Photothermolysis. It targets tissue with a pattern of dispersed spots. This results in a pattern of microscopic zones of tissue coagulation that heal over several weeks while the skin retains normal appearance. Rather than creating a global tissue effect at the surface of the target tissue, or in the dermis alone, this method creates injury in a tiny fraction of the skin treated, coagulating multiple columns of tissue, 70-100 micron in diameter, extending through the epidermis and deep into the dermis reaching up to 1 mm depth. These laser columns create micro thermal zones of tissue coagulation which is surrounded by healthy tissue. The treated zone consists approximately 15-20% of the surface. Tissue is not vaporized and the stratum corneum 10 remains intact. The healthy tissue provides a generous reservoir of stem cells and melanocytes in the papillary dermis that are spared from wounding and accelerate the healing process. The small size of the wounds and the short migratory paths for keratinocytes from the spared tissue result in rapid re-epitheliazation and fast epidermal repair. Zones of collagen denaturation in the dermis cause upregulation of the inflammatory cascade, which leads to collagen remodeling to depths of 400-700 microns resulting in skin tightening. The fact that patients do not have open wounds leads to minimal downtime. Fractional laser resurfacing is therefore a non-ablative procedure offering a gentle yet effective method for skin resurfacing at minimal patient downtime and minimum risk. It offers improved skin texture, tone, pigmentation, fine lines and skin tightening. It claims to be safe for all skin types and can be used on areas other than the face such as the neck, chest and hands which are more delicate and tend to scar. Fractional resurfacing requires a series of 3-5 treatments as opposed to ablative lasers that require a single treatment.
A disadvantage of fractional laser resurfacing is that in order to achieve dramatic results heating of the tissue reaches the temperature in the necrotic zone which is around 70° C., and the tissue, whether it is made up primarily of cells, keratinocytes and their derivatives or collagen, is necrosed or denatured, respectively. Temperatures in the tissue above 100° C. may cause steam to form in the tissue, which may cause disruptive effects. Such temperatures may result in undesirable side effects such as pain, erythema, swelling, occasional scarring, extended healing times and infection.
Thus there is an unmet need for a fractional treatment that causes tissue injury and triggers tissue healing processes but without the risks and complications caused by tissue heating that creates denaturation and coagulation of tissue.
Another method of treating wrinkles includes the use of Botox. Botox is a toxin that is injected into the patient's muscles. The toxin blocks the nerve impulses, temporarily paralyzing the muscles and causing the muscles to relax. As a result wrinkled skin is smoothed out. The smoothing effect is apparent almost immediately and improves over the next few days. Generally the effects of a Botox injection last for between 3 to 6 months depending on the severity of the wrinkles and on the dosage of Botox used.